Water heater control system



Patented Aug. 28, 1945 2,383-675 WATER HEATER CONTROL SYSTEM Clark M. Osterheld, Stoughton, Wia, assignor to McGi-aw Electric Company, Elgin, 111., a corporation of Delaware Application March 20, 1944, Serial No. 527,802

Claims.

My invention relates to electric heating and particularly to control systems for the electric heaters of hot water tanks.

Among the objects of my invention are the following: to provide a water heater control system for the heater of a domestic hot water tank that shall be eflfective to cause energization of the heater immediately upon nightfall in case a relatively large amount of hot water has been withdrawn from the tank during daylight hours and that shall prevent energization oi the heater except after a predetermined period oi time delay in case only a relativelysmall quantity of hot water has been so withdrawn from the tank; to provide a heater control system that shall be effective to cause energization of the electric heater of a domestic hot water tank in case of withdrawal of hot water from the tank during daylight hours.

Other objects of my invention will either be apparent from a description of one control system embodying my invention or will be pointed out in the course of such description and set forth particularly in the appended claims.

In the drawing,

Figure 1 is a vertical section through a domestic hot water tank, having associated therewith a control system embodying my invention, and,

. Fig. 2 is a diagram of connections of my improved control system.

Referring first to Fig. l of the drawing, I have there shown a domestic hotiwater tank I I having a lower cold water inlet pipe I3 and an upper hot water outlet pipe I5. The tank II may be surrounded by a mass ll of heat-insulating material, which material may be held in proper operative position around the tank I I by an outer casing I9. I provide preferably, but not necessarily, a single electric heater 2I which, if only a single electric heater is provided, is preferably positioned around the tank I I adjacent to the lower end thereof and may be positioned in a tunnel member 23. The electricheater II is preferably, but not necessarily,-of a clamp-on type, adapted to be secured in oodheat-conducting relation to the outside surfaceof the tank II adjacent the bottom end portion thereof.

I-providea first thermally-actuable heater control switch; 25, which is shown schematically, or generally only, as comprisinga bimetal bar 21, having one end portion thereof connected to a contact member 29, which is positioned in heatreceiving relation relatively to the tank II just above the heater 2|. Switch 25 includes also a fixed contact member 3|, which is adapted to be which is indicated in Fi 1 of the drawing generally only, and the details of which are to be found in my copending application, S. N. 511,387,

filed November 22, 1943, and assigned to the same assignee as is the present application. Briefly, such thermal retarder includes a first expansion rod 35, which is relatively highly expansible and which is supported in heat-receiving relation relatively to the water in the tank II as by a heatconducting support 31. The thermal retarder 33 includes also a second expansion rod 39, which is of relatively lowthermal expansivity, as compared to rod 35. For illustrative purposes only, the rod 35 may be made of aluminum, while rod 39 may be made of a nickel steel having a thermal expansivity on the order of one-half of that of the high expansion rod 35. The two rods 35 and 39 are adapted to support a switch arm 4|, which is adapted to engage with and be disengaged from a pair of fixed contact members 43 and 45. While no electric insulation has been shown, it is to be understood that such is provided in the design and construction of the thermal retarder 33. The low expansion rod 39 is supported on a block 4'! of heat-insulating material on support 31 and extends substantially parallel axially, relatively to the high expansion rod 35. a

When the temperatures of rods 35 and 39 are on the order of the ordinary room temperature, say 70 F., the lengths of the two rods 35 and 39 will be substantially alike, with the result that the switch and U will be in engagement with contact members 43 and 45. When the thermal retarder 33 is subject to hot water in the tank, the

length of the high expansion rod 35 will be greater than that of rod 39,, with the result that switch arm 4| will be disengaged from contact members 43 and 45.

A low-wattage heating coil 49 is operatively associated with the low expansion rod 39, and after coil 49 has been energized for a predetermined length of time, on the order 01' five or six hours, the temperature of rod 39 will have been raised to a value on the order of 300, with the result that the axial length of rod 39 is again substantially equal to that of rod 35 when rod 35 has been heated to a temperature on the'order of 150 E, which is that of the ordinary hot water in a domestic tank. When the lengths of rods 35mm 39, when heated to 150 F. and 300 F. respectively,

engaged by and disengaged from the bimetal bar are substantially equal, switch arm 4| will again be in engagement with contact members 43 and 45.

While I have illustrated and described a particular form of thermal retarder, I do not desire to be limited thereto, since other thermal retarders effective for the same general purpose, as has been hereinbefore set forth, may be substituted therefor without departing from the spirit and scope of my invention.

A light sensitive cell 5|, here shown generally only as a selenium cell, is provided. This cell 5| is adapted to permit the flow of electric current therethrough when subjected to daylight, and it is to be understood that cell 5| is to be positioned in such manner as to be subject to daylight during'daylight hours.

I provide a pair of supply circuit conductors 53 and 55, and one terminal of cell 5| is adapted to be connected by a conductor 51 with the first supply circuit conductor 53.

I provide an electromagnetic heater control switch designated in its entirety by numeral 59, this switch including, in addition to two fixed contacts 6| and 63, a contact bridging member 65 connected with a magnetizable armature core 61, having an energizing coil 69 wound therearound, all in a manner well known in the art. Switch 59 is adapted to be in closed position when no current is flowing through coil 69 and to be in open position when a current is flowing therethrough. The other terminal of cell 5| is adapted to be connected to one terminal of coil 69, the other terminal of which is connected by a conductor 1| with the second supply circuit conductor 55. When cell 5| is in proper operative condition, the contact bridging member 55 will therefore be in engagement with contacts 5| and 63 during the hours of night and will be out of engagement therewith during daylight hours.

I provide a second electromagnetic switch 13, comprising a pair of fixed contacts and 11, adapted to be engaged by and disengaged from a contact bridging member 19. Contact bridging member 19 is mechanically connected with a magnetizable core 8|, which core is adapted to be energized by a coil 83. One terminal of coil 83 is connected by a conductor 85 to a conductor 81 which connects the second supply circuit con ductor 55 to terminal 29 of the first lower thermally-actuable heater control switch 25.

I provide further a thermal timer 89, comprising a bimetal bar 9|, having one end fixedly secured to a contact terminal 93, while the other free end thereof is adapted to engage with and be disengaged from a contact 95. The thermal timer 89 includes also a heating coil 91 operatively associated with the bimetal bar 9|. One terminal of coil 91 is connected to conductor 1|,

and through this conductor to the second supply circuit conductor 55. Contact terminal 95 of thermal timer 89 is connected by a conductor 99 to the other terminal of cell 5| and of coil 69. Contact 93 is connected by a conductor with the other terminal of coil 83 of the second electromagnetic switch 13. One terminal of heater 2| is connected to contact terminal 3| of the lower heater'control switch 25, while the other terminal of heater 2| is connected by a conductor I93 with fixed contact 15 of the second electromagnetic switch 13. Contact terminal 3| of switch 25 is connected by a conductor I05 with one terminal of heating coil 49 of the thermal retarder 33, the other terminal of heating coil 49 being connected by a conductor ||I1 with contact 43 of the thermal retarder 33, which contact is connected by a conductor I" with contact terminal SI of the first electromagnetic heater control switch 59. The second contact terminal 45 of switch 33 is connected by a conductor I with conductor I93. Fixed contact 11 is connected by a conductor 3 to the first supply circuit conductor 53. Fixed contact 53 is connected to supply circuit conductor 53.

Let it be assumed, for purpose of illustrating the operation of the control system embodying my invention, that heater 2| was energized during night hours, so that at the time when the light sensitive cell 5| became subject to daylight, all of the water in the tank had been heated to a predetermined high temperature, which, as hereinbefore stated, is on the order of 150 F. when all, or substantially all, of the water in the tank had been heated to this high temperature, the bimetal bar 21 moved out of engagement with fixed contact member 3|, with the result that the heater control system was deenergized with attendant deenergization of heater 2|. If this occurred during night hours, contact bridging member would still have been in engagement with fixed contacts 6| and 53 and switch arm 4| would have been in engagement with contact terminals 4| and 43 of the thermal retarder switch 33.

However, when the light sensitive cell 5| became subject to daylight, it would conduct current therethrough, which would result in an energizing current flowing through coil 39 through the following circuit: from supply circuit conductor 53, through conductor 51, cell 5|, coil 69, conductor 1|, and to the second supply circuit conductor 55. This would energize core 81 and cause lifting of the contact bridging member 65 out of engagement with contacts BI and 63; whereby, as will be evident from inspection of the connections shown in Fig. 2, the circuit comprising heater 2| would be opened.

Let it now be assumed that hot water is used in the early daylight hours, with the result that the lower thermal switch 25 is subject to cold water, with the result that bimetal bar 21 would move into engagement with contact 3|. This, however, would not have any other effect because of the disengagement of contact bridging member 55 with contacts 6| and 63. However, an energizing circuit will be closed through heating coil 91 of the thermal timer 33, which energizing circuit may be traced as follows: from the first supply circuit conductor 53, through conductor 51, light sensitive cell 5|, conductor 99, coil 91, and from and through conductor 1| to the second supply circuit conductor 55 It may be here noted that the wattage of heating coil 91 is relatively small so that it will require from say five to six hours before the bimetal bar 9| will have been heated sufiiciently to cause it to move into engagement with fixed contact member 95. Thus, it hot water was withdrawn from the tank at say 7 a. m., the quantity withdrawn being sufiicient to cause the entry of enough cold water into the bottom end of the tank to subject switch 25 thereto, bimetal bar 9| would be moved into engagement with contact 95 at a time on the order of 12 noon or 1 p. m.

current will cause a raising of the core 3|, with the attendant result that contact bridging member I9 will be moved into engagement with contacts I and 11 so that an energizing circuit through heater 2| is closed, which circuit may be traced as follows: from supply circuit conductor 55, through conductor 81. through the closed lower switch 25, heater 2|, conductor I03. contacts 15 and I1, and contactbridging member 13, and through conductor H3 to the other supply circuit conductor 53.

It is evident that energization of heater 2| of the not water tank II will be delayed for a length of time, during daylight hours, that will cause its energization to take place during the ofl-peak daylight period, which generally speaking, is usually to be found to occur at, or shortly after, 12 noon. The lengthof time during which energization of the heater 2| will continue, depends, of course, upon the amount of cold water which entered the tank to replace the hot water used from the tank; but when substantially all of the water in the tank is hot, bimetal bar 21 of the thermal switch 25 will interrupt the circuit.

Let it now be assumed that a relatively small quantity of hot water is drawn from tank I| during the early night hours, during which time contact bridging member 65 will be in engagement with contacts 6| and 63. If only the lower thermal switch 25 is subject to cold water, an energizing circuit through heating coil 49 will be effected, which circuit may be traced as follows: from supply circuit conductor 53, through the engaged contact bridging member 65 and contacts BI and 63, through conductors I09 and I01, coil 49, through conductor H15, through the lower thermal heater control switch 25, and from and through conductor 81 to the second supply circuit conductor 55. As has been hereinbefore set forth, the length of time required to cause temperature rise of the low expansion rod 39 to a temperature on the order of 300 F. is five to six hours, so that in case say bimetal bar 21 was moved into engagement with contact 3| at 7 p. m., with attendant energization of coil 43 at that time, it would be 12 midnight or 1 a. m. before switcharm 4| would again be moved into engagement with contacts 43 and 45. Energization of heater 2| will then be efiected and will continue until substantially all of the water in the tank is hot, when movement of bimetal bar 21 into open position will take place, with attendant deenergization of heater 2|.

Let it now be assumed that a relatively large amount of hot water was withdrawn from the tank during the early evening or night hours, so that the thermal retarder switch 33 .will also be subject to cold water, This will result in contraction of the high expansion rod 35, with attendant movement of switch arm 4| into closed position, that is into engagement with contact terminals 43 and 45. This will close energizing circuit through heater 2|, which circuit may be traced as follows: from supply circuit conductor 55, through conductor 81, through the lower switch 25, heater 2|, conductors I03 and Ill, through the closed thermal retarder switch comprising contact terminals 45 and 43 and switch arm 4|, through conductor I09, to the engaged contacts 5| and 63 and contact bridging member 55, and to the other supply circuit conductor 53.

In other words, if a relatively large quantity of hot water has been withdrawn from the tank during the early evening or night hours, energization of the heater 2| will occur simultatarder heater control switch 33 to cold water, and such energization will continue until the thermal retarder switch is again subject to hot water, when the switch arm 4| will be moved out of engagement with contact terminals 43 and 45, provided that the heating coil 49 has not been energized longenough to cause temperature rise of the second low expansion rod 39 to a length sufllcient to maintain switch arm 4| in engagement with contacts 43 and 45; but when coil 49 has been energized for a length of time on the order of five to six hours, the second expansion rod 39 will have been raised to a temperature suflicient to cause its length to again be substantially the same as that of the first expansion rod 35, with attendant closure of the switch controlled by the two thermally-expansible rods. Closure of the thermal retarder switch will again cause energization of heater 2| through the circuit hereinbefore described, which energization will continue until substantially all of the water in the tank is hot, when the lower thermallyactuable switch 25 will causddeenrgization of heater 2| in the manner hereinbefore described.

Various modifications may be made in the system embodying 'my invention without departing from the spirit and scope thereof, and all such modifications coming clearly within the scope of the appended claims shall be considered as cov' ered. thereby.

I claim as my invention:

1. A controlsystem for an electric heater for a hot water tank, comprising a. main thermallyactuable heater control switch subject to tank water temperature at the lower end portion of the tank and adapted to be in closed position when subject to cold water, a second heater control switch means controlled by a light-sensitive cell to be in open position during daylight hours and in closed position during night hours, a third heater control switch electrically connected in shunt circuit relation to said second switch and adapted to be normally in open position, and a thermal timer means effective to cause movement or said third switch into closed position to efiect energization of said heater with a predetermined time period of delay after daybreak in case said main switch is subject to cold water at daybreak.

2. A control system for an electric heater for a hot water tank, comprising a main thermallyactuable heater controlswitch subject to tank water temperature at the lower end portion. of the tank and adapted to be in closed position when subject to cold water, a second heater control switch means controlled by a light-sensitive cell to be in open position during daylight hours and in closed position during night hours, a third heater control switch electrically connected in shunt circuit relation to said second switch and adapted to be normally in open position and a thermal timer means efl'ective to cause movement of said third switch into closed position to effect energization or said heater with a predetermined time period of delay after said main switch becomes subject to cold water during daylight hours.

3. A control system for an electric heater for a hot water tank, comprising a main thermallyactuable heater control switch subject to tank water temperature at the lower end portion of the tank and adapted to be in closed position when subject to cold water, a second heater control switch controlled by a light sensitive cell neously with the subjection of the thermal reto be in open position during daylight hours, a thermal retarder heater control switch subject to tank water temperature intermediate the ends of the tank connected in series circuit with said main and said second switch, said thermal retarder switch being selectively eflective during night hours to cause energization of said heater with a time period of delay and immediately in accordance with the amount of cold water in the tank, an. electromagnetic switch connected in shunt circuit relative to said second and said thermal retarder switch and a thermal timer means"controlled by said light sensitive cell to cause closing of said electromagnetic switch and energization of said electric heater with a predetermined time period of delay after said main switch becomes subject to cold water during thetrol switch subject to tank water temperature intermediate the ends of the tank adapted to bein closed position when subject to cold water in the tank and adapted to be moved into closed position with a predetermined time period of delay when subject to hot water in the tank, a third heater control switch connected in series circuit with said first and said second switch and said heater, a light sensitive cell for controlling said third swltch to be open during daylight hours and closed during night hours, a fourth heater control switch connected in shunt circuit to said second and third switches and a thermal timer means controlled by said light sensitive cell to cause closure of said fourth switch and attendant energization of said heater with a predetermined time period of delay during daylight hours in case said first switch is subject to cold water during daylight hours.

5. A control system as set forth in claim 4, in which said first switch is effective to deenerglze the heater when substantially all of the water in the tank is hot.

CLARK M. OS'I'ERHELD. 

